1. Field of the Invention
The present invention relates, in general, to heat pump systems and, more particularly, to a heat pump system that uses air as its heat source.
2. Description of the Prior Art
As well known to those skilled in the art, a heat pump system is an air conditioning machine that is selectively used as a heater or a cooler by changing the refrigerant flowing direction in the system, as desired. That is, in a conventional heat pump system, a main refrigerant line starting from the outlet port of a compressor extends while sequentially connecting a four-way valve, an indoor heat exchanger, two expansion valves, and an outdoor heat exchanger to each other, prior to being ended at the four-way valve. In addition, the four-way valve is also connected to the inlet port of the compressor through a refrigerant suction line. During a heating mode operation of the heat pump system, the four-way valve controls the refrigerant flowing direction in the main refrigerant line such that high pressure and high temperature gas refrigerant outputted from the compressor flows to the indoor heat exchanger, which acts as a condenser for condensing the gas refrigerant while transmitting heat from the gas refrigerant to indoor air or water flowing around the indoor heat exchanger, thus heating the indoor air or producing hot water while condensing the gas refrigerant. In such a case, the heat pump system performs a heating, drying or hot water producing function. The high pressure and high temperature liquid refrigerant outputted from the indoor heat exchanger is expanded in the heating mode expansion valve. The refrigerant from the expansion valve is, thereafter, evaporated by heat at the outdoor heat exchanger acting as an evaporator using outdoor air as a heat source. At the outdoor heat exchanger, the liquid refrigerant thus becomes low pressure and low temperature gas refrigerant, which is returned to the compressor so as to accomplish one cycle. During the heating mode operation, the heat pump system repeats the above-mentioned cycle.
During a cooling mode operation of the heat pump system, the four-way valve controls the refrigerant flowing direction in the main refrigerant line such that the high pressure and high temperature gas refrigerant outputted from the compressor flows to the outdoor heat exchanger, which acts as a condenser for condensing the gas refrigerant while transmitting heat from the gas refrigerant to outdoor air used as a heat source of the condenser. At the outdoor heat exchanger, the high pressure and high temperature gas refrigerant thus becomes high pressure and high temperature liquid refrigerant, which is outputted to the cooler-mode expansion valve so as to be expanded in the expansion valve. The liquid refrigerant from the cooling mode expansion valve is evaporated by heat transmitted from indoor air or water, at the indoor heat exchanger acting as an evaporator. In such a case, due to the evaporation of the refrigerant at the indoor heat exchanger, the refrigerant absorbs heat from the indoor air or water flowing around the indoor heat exchanger, thus cooling the indoor air or producing cold water. At the indoor heat exchanger, the refrigerant thus becomes low pressure and low temperature gas refrigerant, which is returned to the compressor so as to accomplish one cycle. During the cooling mode operation, the heat pump system repeats the above-mentioned cycle.
During an evaporation of the liquid refrigerant using heat of outdoor air at the outdoor heat exchanger in a heating mode operation of the conventional heat pump system, moisture laden in the outdoor air may be frozen on the external surface of the outdoor heat exchanger when the temperature of the outdoor air is excessively low. In such a case, the frost formed on the external surface of the outdoor heat exchanger reduces the evaporation effect of the liquid refrigerant, thus remarkably reducing the heating capacity of the heat pump system. Therefore, the technique of promoting the evaporation of liquid refrigerant at the outdoor heat exchanger or promoting the evaporation of gas refrigerant inputted into the compressor of heat pump systems has been actively studied.
For example, Japanese Patent Laid-open Publication No. Sho. 54-45949 discloses an air conditioning apparatus, with a refrigerant heater installed on the refrigerant line of the apparatus and used as an evaporator during a heating mode operation of the apparatus. In a heating mode operation of the above Japanese air conditioning apparatus, high pressure and high temperature refrigerant outputted from a compressor is condensed at an indoor heat exchanger while heating indoor air. The refrigerant is, thereafter, dropped in its pressure at a heating mode pressure reducer, and evaporated at the refrigerant heater. Therefore, this air conditioning apparatus is not deteriorated in its heating capacity even when the apparatus is operated as a heater in cold outdoor air. In addition, Japanese Patent Publication No. Sho. 55-5017 discloses a heat pump type air conditioning apparatus, which has a plurality of outdoor heat exchangers, and a flow control unit. The flow control unit switches the refrigerant flow between a first cycle, in which the outdoor heat exchangers act as condensers at the same time in the case of a cooling mode operation, and act as evaporators at the same time in the case of a heating mode operation, and a second cycle, in which a part of high temperature gas refrigerant directly flowing from a compressor to an indoor heat exchanger is fed to the outdoor heat exchangers so as to allow one of the outdoor heat exchangers to alternately act as a condenser and an evaporator and, at the same time, allow the other outdoor heat exchanger to alternately act as an evaporator and a condenser. Another example of conventional heat pump systems is referred to U.S. Pat. No. 6,050,102, allowed to the inventor of the present invention and entitled xe2x80x9cheat pump type air conditioning apparatusxe2x80x9d. This heat pump type air conditioning apparatus comprises a compressor, a four-way valve, an indoor heat exchanger, a cooling mode capillary tube used as a pressure reducer, a heating mode capillary tube used as a pressure reducer, and an outdoor heat exchanger connected to each other by both a first refrigerant line and a gas refrigerant suction line. The above heat pump type air conditioning apparatus also has a first heat exchanger and a second heat exchanger. The first heat exchanger is installed on the first refrigerant line at a position between the indoor heat exchanger and the heating mode capillary tube. The second heat exchanger is installed on the first refrigerant line at a position between the outdoor heat exchanger and the four-way valve such that the second heat exchanger is positioned higher than the first heat exchanger. The second heat exchanger is also connected to the first heat exchanger through a connection line having an on-off valve, such that the first and second heat exchangers form a closed circuit. The first and second heat exchangers contain actuation fluid therein and vaporize both the remaining liquid refrigerant and incompletely vaporized gas refrigerant from the outdoor heat exchanger using the actuation fluid heated and vaporized by liquid refrigerant from the indoor heat exchanger.
In an operation of such a conventional heat pump system, liquid or gas refrigerant is evaporated or condensed at the outdoor heat exchanger using heat of outdoor air, and so the thermal capacity of the system is determined by the quantity of heat transmitted at the indoor heat exchanger. Typically, it has been well known to those skilled in the art that the heat exchanging surface area of the outdoor heat exchanger, determining the thermal capacity of the system, is set to about 1.2 to 1.4 times larger than that of the indoor heat exchanger.
In Japanese Patent Laid-open Publication No. Sho. 54-45949, it is described that a refrigerant heater is installed on the refrigerant line, and is used as an evaporator during a heating mode operation. However, this Japanese patent does not disclose the technical construction of the refrigerant heater in detail. Due to an intrinsic structural limitation of typical evaporators, it is inevitable that the refrigerant heater has a structure, limiting the volume of the refrigerant heater and allowing an easy installation of the refrigerant heater in an air conditioning apparatus. However, such a structure of the refrigerant heater undesirably increases the maintenance cost of the air conditioning apparatus. The heat pump type air conditioning apparatus disclosed in Japanese Patent Publication No. Sho. 55-5017 is disadvantageous as follows: That is, this apparatus is designed such that the external surface of the outdoor heat exchanger is defrosted by heat of a part of high pressure and high temperature output refrigerant of a compressor during a heating mode operation in cold outdoor air. Therefore, it is necessary to use a large capacity compressor, which undesirably increases the production cost and maintenance cost of the apparatus. The heat pump type air conditioning apparatus of U.S. Pat. No. 6,050,102, allowed to the inventor of this invention, is problematic in that liquid refrigerant cannot be desirably evaporated at the outdoor heat exchanger when the temperature of outdoor air is low, and it is necessary to use an additional heater for heating refrigerant at the outdoor heat exchanger during an operation in the coldest weather, and so the apparatus has a complicated construction and high production and maintenance costs. Furthermore, during a heating mode operation of the conventional heat pump type air conditioning apparatuses in the coldest weather, liquid refrigerant cannot be desirably or completely vaporized at the outdoor heat exchanger, and so the coefficient of performance (COP) of such air conditioning apparatuses is reduced. Such a reduction in COP results in a degradation of thermal efficiency of the apparatuses.
During a cooling mode operation of the conventional heat pump systems in hot outdoor air, there is only a small difference in the temperature between the outdoor air and gas refrigerant to be condensed at the outdoor heat exchanger, and so the gas refrigerant may be incompletely condensed at the outdoor heat exchanger. In such a case, the liquid refrigerant may be incompletely vaporized at the indoor heat exchanger when the cooling load imposed on the indoor heat exchanger acting as an evaporator during such a cooling mode operation is reduced. Therefore, there occurs a liquid back, in which refrigerant in the form of wet vapor is returned to the compressor and sometimes causes damage to the valve of the compressor. In the case of occurrence of such a liquid back, there occurs a liquid hammer in the compressor while compressing the refrigerant in the form of wet vapor. A reduction in COP may occur, and in addition the compressor may be severely damaged or broken.
Such problems experienced in the conventional heat pump systems may be overcome by increasing the thermal capacity of outdoor heat exchangers. However, such an increase in the thermal capacity of the outdoor heat exchangers undesirably increases the production cost, and requires an enlarged installation area of the systems.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a heat pump system, which effectively and completely vaporizes liquid refrigerant at its outdoor heat exchanger during a heating mode operation in cold outdoor air, and effectively completely condenses gas refrigerant at its indoor heat exchanger during a cooling mode operation in hot outdoor air, thus increasing COP.
Another object of the present invention is to provide a heat pump system, which completely vaporizes the wet vapor refrigerant returned to a compressor, thus changing the phase of the input refrigerant of the compressor to a dry vapor phase or a superheated vapor phase.
In order to accomplish the above objects, the present invention provides a heat pump system, comprising: a basic refrigeration circuit consisting of: a main refrigerant line starting from a compressor, and extending while sequentially connecting a four-way valve, an indoor heat exchanger, a cooling mode expansion valve, a heating mode expansion valve and an outdoor heat exchanger to each other, prior to being ended at the four-way valve; and a refrigerant suction line extending from the four-way valve to the compressor; a heat accumulator containing both a heat medium and a heat storage phase change material therein, and mounted on the main refrigerant line at a position between the cooling mode expansion valve and the heating mode expansion valve; a heat-dissipating heat exchanger mounted on the main refrigerant line, and set in the accumulator by allowing the main refrigerant line to pass through the heat accumulator; a subsidiary heat exchanger installed at a position around the inlet port of the outdoor heat exchanger and connected to the heat accumulator through heat medium feed and return lines, with a circulating pump mounted on the heat medium return line; a heat pipe consisting of: an evaporating part installed at the periphery of the heat-dissipating heat exchanger; and a heat dissipating part installed at the periphery of the heat accumulator, and connected to the evaporating part through a connection pipe; and first and second heat-absorbing heat exchangers connected to the refrigerant suction line in parallel to each other such that the first heat-absorbing heat exchanger is set in the heat dissipating part, and the second heat-absorbing heat exchanger is set in the heat accumulator, the first and second heat-absorbing heat exchangers being selectively operated in accordance with the temperature of refrigerant flowing through the suction line to be returned to the compressor.